GH-3428: Make Kotlin dependency optional again

Fixes https://github.com/spring-projects/spring-integration/issues/3428

The Kotlin Gradle plugin starting with Kotlin `1.4` adds a standard
Kotlin lib into `compile` scope fully ignoring an `optional` variant.
See more info here: https://kotlinlang.org/docs/reference/using-gradle.html#dependency-on-the-standard-library

* Add `kotlin.stdlib.default.dependency=false` into `gradle.properties`
to rely only on the explicit dependency definitions in the project config
* Remove explicit Kotlin deps from test scope in the target modules since
it is declared globally for all the modules
* Fix author emails in the `publish-maven.gradle` to their VMware variants
* Remove usage of `org.jetbrains.annotations` in favor of `@Nullable`
from Spring Framework

build.gradle

@@ -603,8 +603,6 @@ project('spring-integration-kafka') {
 
 		testImplementation "org.springframework.kafka:spring-kafka-test:$springKafkaVersion"
 		testImplementation "com.willowtreeapps.assertk:assertk-jvm:$assertkVersion"
-		testImplementation 'org.jetbrains.kotlin:kotlin-reflect'
-		testImplementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8'
 		testImplementation "org.hamcrest:hamcrest-core:$hamcrestVersion"
 
 		testRuntimeOnly 'com.fasterxml.jackson.core:jackson-core'

gradle.properties

@@ -2,3 +2,4 @@ version=5.4.1-SNAPSHOT
 org.gradle.jvmargs=-Xmx1536m -Dfile.encoding=UTF-8
 org.gradle.caching=true
 org.gradle.parallel=true
+kotlin.stdlib.default.dependency=false

publish-maven.gradle

@@ -30,19 +30,19 @@ publishing {
 					developer {
 						id = 'abilan'
 						name = 'Artem Bilan'
-						email = 'abilan@pivotal.io'
+						email = 'abilan@vmware.com'
 						roles = ["project lead"]
 					}
 					developer {
 						id = 'garyrussell'
 						name = 'Gary Russell'
-						email = 'grussell@pivotal.io'
+						email = 'grussell@vmware.com'
 						roles = ["project lead emeritus"]
 					}
 					developer {
 						id = 'markfisher'
 						name = 'Mark Fisher'
-						email = 'mfisher@pivotal.io'
+						email = 'markfisher@vmware.com'
 						roles = ["project founder and lead emeritus"]
 					}
 				}

spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/config/StoredProcParserUtils.java

@@ -21,7 +21,6 @@ import java.util.List;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-import org.jetbrains.annotations.NotNull;
 import org.w3c.dom.Element;
 
 import org.springframework.beans.BeanMetadataElement;
@@ -148,7 +147,6 @@ public final class StoredProcParserUtils {
 		}
 	}
 
-	@NotNull
 	private static BeanDefinitionBuilder createParameterBeanDefinitionBuilder(Element storedProcComponent,
 			ParserContext parserContext, String direction, String returnType) {
 

spring-integration-redis/src/main/java/org/springframework/integration/redis/inbound/RedisQueueInboundGateway.java

@@ -19,8 +19,6 @@ package org.springframework.integration.redis.inbound;
 import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
 
-import org.jetbrains.annotations.Nullable;
-
 import org.springframework.beans.factory.BeanClassLoaderAware;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
@@ -39,6 +37,7 @@ import org.springframework.integration.util.ErrorHandlingTaskExecutor;
 import org.springframework.jmx.export.annotation.ManagedMetric;
 import org.springframework.jmx.export.annotation.ManagedOperation;
 import org.springframework.jmx.export.annotation.ManagedResource;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessagingException;
 import org.springframework.scheduling.SchedulingAwareRunnable;

spring-integration-stomp/src/main/java/org/springframework/integration/stomp/AbstractStompSessionManager.java

@@ -27,7 +27,6 @@ import java.util.concurrent.atomic.AtomicInteger;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-import org.jetbrains.annotations.NotNull;
 
 import org.springframework.beans.factory.BeanNameAware;
 import org.springframework.beans.factory.DisposableBean;
@@ -215,7 +214,6 @@ public abstract class AbstractStompSessionManager implements StompSessionManager
 		}
 	}
 
-	@NotNull
 	private CountDownLatch addStompSessionCallback(int currentEpoch) {
 		CountDownLatch connectLatch = new CountDownLatch(1);
 		this.stompSessionListenableFuture.addCallback(